The present invention relates to a device and method for measuring fluid flow and, in particular, relates to a device and method for measuring instantaneous fluid flow within a vessel characterized by a fluctuating elastic wall. One example of such a vessel is an arterial vessel.
A significant challenge to modern medicine concerns accurate measurement of instantaneous blood flow through an arterial vessel. Accurate measurements of such blood flow would contribute to enhanced assessment of vascular status and improved diagnosis of a variety of vascular diseases. Improved diagnosis and enhanced assessment of vascular status should facilitate more effective disease treatments.
Another major challenge is the measurement of instantaneous flow into various distinct regions or portion of pulmonary vasculature.
Several methods for measuring blood flow are already available to the art. One method involves measurement of blood flow by placing an electromagnetic flow meter around a blood vessel or on a graft. Such a method has been generally limited to blood flow measurements during surgery. The method also undesirably requires surgical access to the exterior of the blood vessel or installing a graft.
Another method for measuring blood flow involves attaching a Doppler crystal to the end of the catheter and maneuvering the end of the catheter into the artery. The various Doppler crystal systems provide accurate blood velocity information. But as a method for flow measurement, Doppler systems are limited by measuring velocity but not cross-sectional area. Consequently, measurements of velocity may not reflect true volumetric flow if the arterial wall is elastic. Most arteries, however, are characterized by elastic walls and because cardiac output is pulsed into the elastic walls and arteries are muscular tubes that have a variable amount of tone. Hence, the cross-section of the artery fluctuates. Since flow is a function of both fluid velocity and cross-sectional area, improved velocity measurements fail to improve the measurement of flow.
Because the pulmonary arteries are thin and very elastic, a particularly challenging problem in blood flow measurement concerns the measurement of flow to various portions or segments of the vasculature serving the lungs. There have been suggestions that dysfunctions in the vasculature; for example, hypertension, sclerosing, or occluding of arteries, tends to occur heterogeneously rather than homogeneously within the lungs. Further, it has been suggested that blood flow has a tendency to favor lower regions or portions of the lungs relative to upper portions of the lungs, in a gravity dependent fashion. To date, however, most pulmonary blood flow assessments have been performed on the entire pulmonary blood flow rather than a localized region of the lung.
Catheters capable of maintaining a constant position within an artery are known, however, such catheters do not stabilize the cross-sectional area within the artery.